Project Summary Eukaryotic genomes are plagued with selfish DNA sequences that can have a negative impact health. Meiotic drivers are one type of these DNA parasites that exploit gametogenesis to bias their own transmission into the next generation. Instead of being transmitted to half the gametes generated by heterozygous individuals, meiotic drivers cheat the process to be found in up to 100% of the functional gametes. This selfish behavior imposes a heavy burden on the organism. Meiotic drivers can directly cause infertility by killing gametes that do not inherit them. Meiotic drivers can also contribute to diseases or infertility indirectly by promoting the maintenance and spread of deleterious alleles in a population. Although meiotic drivers are widespread in eukaryotes, including humans, few meiotic drive alleles have been cloned and very little is known about the molecular mechanisms they use to cause drive. In addition, there are few controlled experimental analyses of how these selfish genes spread within genomes and populations. This proposal exploits an innovative model system for studying meiotic drive, the wtf family of drivers in fission yeast. Driving wtf genes act by generating both a poison and an antidote from alternate transcripts. All the gametes are poisoned, but those that inherit the wtf allele are rescued by the antidote. The proposed experiments use a multidisciplinary approach to dissect the molecular mechanisms of how the poison protein is delivered to developing gametes, how the poison kills cells, and how the antidote neutralizes the poison. In addition, the experiments will address major questions in the evolution of meiotic drive genes. The proposed work will determine how poison and antidote specificity is maintained as the selfish wtf genes duplicate and diverge within a genome. This question is especially important given that disrupting poison and antidote specificity causes severe infertility, yet the selfish genes rapidly diverge. The work also develops the first assay for high-throughput experimental evolution analyses of meiotic drivers to explore questions about how these parasites (and linked variants) spread in a population. This assay will provide experimental tests of current theoretical models and test more complex real-world scenarios not currently described by such models. This work will provide essential molecular and evolutionary characterization of a model meiotic driver that will help guide discovery and analyses of analogous selfish loci in more complex eukaryotes, including humans. This expanded understanding DNA parasites should ultimately lead to improved reproductive outcomes in humans.